NATURAL SELECTION AND VARIATION Part 1
THE WORK OF CHARLES DARWIN
EVOLUTION AS A (SCIENTIFIC) THEORY Evolution change in a population of organisms over time Scientific Theory well-tested explanation based on evidence that unifies as broad range of observations and hypotheses Law has a mathematical equation to explain it Evolution is considered a theory as ALL evidence supports the idea that organisms have changed and continue to change, over time
CHARLES DARWIN Lived in England 1809-1882 1831-1836: Beagle s five-year voyage mapping the coastline of South America 1859: On the Origin of Species by Means of Natural Selection EVOLUTION explains how modern organisms evolved over long periods of time through descent from common ancestors
DARWIN S VOYAGE
WHAT DARWIN KNEW What did Darwin (and science) know? The Earth is REALLY old 4.6 Billion Years The Earth has changed over time Mountains and valleys formed Rivers change course Water erodes land Humans can change organisms through breeding Organisms have rapid Population Growth Darwin realized most organisms don t survive and reproduce???which individuals survive and why???
WHAT DARWIN DIDN T KNOW DNA and Genetics Knew that traits were passed from parent to offspring Didn t know HOW Most of what you learned last semester!
Inherited Characteristics List the characteristics that you believe you have always had. For example, you may have brown eyes or curly hair. Acquired Characteristics List your acquired characteristics. For example, you may have learned how to play a musical instrument.
Jean Baptiste Lamarck proposed theory of evolution based on growing fossil record Suggested that organisms could change during their lifetimes by selectively using or not using various parts of their bodies. Suggested that individuals could pass these acquired traits onto offspring, enabling species to change over time Published ideas in 1809 year Darwin was born
If Lamarck was correct, offspring would inherit acquired trait of parent = no tail parent mouse Tail is removed to simulate disuse of characteristic during lifetime offspring mouse BUT offspring have tails
Lamarck was INCORRECT because: 1. Organisms do not have an inborn drive to be perfect 2. Evolution does not mean that over time species becomes better somehow 3. Evolution does not progress in predetermined direction 4. Traits acquired by organisms during lifetime cannot be passed on to offspring Lamarck gave us some good stuff too! Lamarck was one of 1 st to try to explain evolution scientifically using natural processes Recognized link b/w org s environment and body structures
THE FOSSIL RECORD Fossils: preserved remains or markings left by organisms that lived in the past Sand and silt is eroded from land and settles in the bottom bodies of water Layers pile up and form rock strata Bodies get buried in layers and become fossils Fossils can also occur on land under volcanic ash or dust
THE FOSSIL RECORD Younger strata are layer on top of older ones Positions of fossils in rock strata can give us relative age Fossil Record: chronological collection of life s remains in the rock layers, recorded during the passage of time Fossils show that life on earth is changing
THE FOSSIL RECORD Oldest fossil found: 3.8 billion years old Fossils of extinct species help us reconstruct the past Fossil evidence supports cellular and molecular evidence of Earth s history Whale fossils from 40 billion years ago show that whales had hind-limb bones Supports theory that whales evolved from ancestors with 4 limbs
SPECIES VARY OVER TIME Darwin noticed that some fossils of extinct animals were similar to living species Glyptodont giant armored animal found in area where current armadillo is found Armadillo = smaller version of glyptodont
NATURAL SELECTION
STRUGGLE FOR EXISTENCE If more individuals are produced than can survive members of a population must compete to obtain food, living space, and other limited necessities of life Called: Struggle for Existence Which individuals come out on top of struggle?
VARIATION AND ADAPTATION Individuals have natural variations among heritable traits Some variants are better suited to life in their environment than others Predatory species that are faster, longer claws, sharper teeth catch more prey Prey species that are faster, better camouflaged avoid being caught
SOME VARIATIONS ARE FAVORABLE Adaptation - any heritable characteristic that increases an organism s ability to survive and reproduce body parts or structures bear s claws body color camouflage or mimicry physiological functions a plant carrying out photosynthesis behaviors avoidance strategies prey use crane flapping wings
Overproduction DARWIN S OBSERVATIONS Variation Darwin realized that species tend to produce excess offspring limit resources + excess offspring = competition Not Everyone Survives! Differences among members of the same species Most variation is heritable Siblings look more like each other than they do other people
DARWIN S OBSERVATIONS
NATURAL SELECTION AND SPECIES FITNESS Overtime, natural selection results in changes in the inherited characteristics of a population. These changes increase a species fitness survival rate
SUMMARY OF DARWIN S THEORY 1. Organisms differ; variation is inherited 2. Organisms produce more offspring than survive 3. Organisms compete for resources 4. Organisms with advantages survive to pass those advantages to their children 5. Species alive today are descended with modifications from common ancestors
ARTIFICIAL SELECTION Artificial Selection: selective breeding of domesticated plants and animals to produce offspring with genetic traits that humans value nature provides variation, humans select variations that are useful. Example: a farmer breeds only his best livestock
ARTIFICIAL SELECTION Humans have been modifying species for thousands of years Darwin saw this being done with dogs He observed that a species could be changed a lot in a short period of time Thought that the same thing could be happening in nature at a slower pace
DIFFERENCES Natural Selection Traits that are more beneficial in the organisms environment become more common in the population Artificial Selection Humans choose the traits that become more common in the population
PESTICIDES: NATURAL SELECTION IN ACTION Pesticides are used to kill insects in crops and homes Insects evolve resistance to pesticides over time High doses and more potent pesticides are needed to be used In the 1950 s only small amounts of the pesticide malathion were used Today insects are resistant to very high concentrations of malathion
PESTICIDE RESISTANCE
Natural selection does not make orgs better Adaptations don t have to be perfect just good enough to enable org to pass its genes to next generation doesn t have to move in fixed direction no one perfect way of doing something If local env changes traits that were once adaptive may no longer be useful and different traits may become adaptive If env changes faster than species can adapt = extinct
COMMON DESCENT Natural selection depends on ability of orgs to reproduce Every org alive today is descended from parents who survived and reproduced Living species are descended with modification from common ancestors (descent with modification) Implies life has been on Earth for very long time Used fossil record for evidence
Darwin based explanation for diversity of life on idea that species change over time Implies that all organisms are related Common ancestor shared by tigers, panthers, cheetahs Common ancestor shared by these felines and horses, then bats Farther back all mammals share ancestor with birds, alligators, fish According to the principle of common descent, all species living and extinct are descended from common ancestors
EVIDENCE OF EVOLUTION
BIOGEOGRAPHY Study of where organisms live now vs. where their ancestors lived in the past Patterns in the distribution of living and fossil species tell us how modern orgs evolved from their ancestors Two patterns: closely related species differentiate in slightly different climates very distantly related species develop similarities in similar environments Pangolins!
PLATES OF THE EARTH
CONTINENTAL DRIFT
CLOSELY RELATED BUT DIFFERENT Galápagos species evolved from mainland species natural selection produced variations that resulted in different, but closely related, island species Ex: variation in shell shape among the giant land tortoises
DISTANTLY RELATED BUT SIMILAR similar global habitats, home to species distantly related similarities among those animals similar selection pressures had caused different species to develop similar adaptations Differences in body structures among those animals provide evidence that they evolved from different ancestors Ex: similar ground-dwelling birds (rheas, ostriches, and emus) inhabit similar grasslands in Europe, Australia, and Africa
THE AGE OF EARTH Evolution takes a long time if such complex life has evolved, then Earth must be very old Radioactive dating Earth is about 4.5 billion years old plenty of time for evolution by natural selection
24 HOUR DAY ANALOGY
COMPARING ANATOMY Evolution homologous structures adapted to different purposes Result of descent w/ modification from common ancestor All vertebrate limbs had the same basic bone structure Some were used for crawling, some for climbing, some for running, others for flying similarities and differences help determine how recently two species shared a common ancestor
HOMOLOGOUS STRUCTURES Biologists study anatomical details, embryos, and evolutionary pattern to see if they are homologous Plants can share homologous stems, roots, and flowers These limbs evolved, with modifications, from the front limbs of a common ancestor whose bones resembled those of an ancient fish.
ANALOGOUS STRUCTURES Body parts that share common function, not structure Clue to common descent is common structure, not common function Ex: bird s wing and a horse s front limb have different functions but similar structures (homologous) wing of a bee and the wing of bird, same function but different structure (analogous)
RECENT FOSSIL FINDS Paleontologists have discovered hundreds of fossils that show stages in the evolution of modern species Other recent fossil finds connection between dinosaurs and birds; fish and four-legged land animals
RECENT FOSSIL FINDS Here is evolution of whales from ancient land mammals
VESTIGIAL STRUCTURES Inherited from ancestors, but have lost much or all of their original function due to different environmental pressures Presence does not affect organism s fitness so natural selection does not act to eliminate it Ex: hipbones of baleen whales Ex: legs of three-toed skink Ex: wings of a flightless cormorant
EMBRYOLOGY Early developmental stages of vertebrates look very similar Same groups of embryonic cells develop in same order and in similar patterns to produce many homologous tissues and organs in vertebrates Further evidence that organisms have descended from a common ancestor Evolution offers the most logical explanation for these similarities
LIFE S COMMON GENETIC CODE All living cells use info coded in DNA to carry info from one generation to the next DNA is nearly identical in almost all organisms, including bacteria, yeasts, plants, fungi, and animals
HOMOLOGOUS MOLECULES Homology not limited to physical structures Homologous proteins share extensive structural and chemical similarities Example: cytochrome c cellular respiration found in almost all living cells Homologous genes makes sense b/c all animals share same code Example: Hox genes determine headto-tail axis in embryonic development found in almost all multicellular animals Living organisms evolved through descent with modification from a common ancestor
GENETICS AND MOLECULAR BIOLOGY Example: Hemoglobin Differences